If you’ve read any of my tips on eating for gut health, you’ll know that wholegrain carbs (like porridge oats, wholemeal bread and brown rice) contain more food for your gut microbes than white versions like white bread and white pasta. That’s because wholegrain varieties are higher in fibre, which we don’t digest. Instead fibre skips digestion and lands in the large intestine, where it provides energy for your gut microbes and helps them thrive.
But what about the idea that leftover cold pasta - and other cooked and cooled carbs like rice and potatoes - might contain more fuel for your gut microbes than the freshly cooked kind? Let me explain.
It’s all about the starch
Most of the energy in pasta, rice, potatoes, and bread comes from carbohydrates, along with a small amount of protein and a little fibre. The majority of this carbohydrate is in the form of starch, made up of long chains of glucose. When we eat carbohydrate-rich foods like pasta, the starch is broken down into individual glucose units. These are absorbed into the bloodstream and used by your body for energy.
Raw starch is difficult to digest because it’s tightly packed in teeny tiny granules, which is why we cook starchy foods before eating them. And here's where it gets interesting: when starchy foods are cooked with water (as with pasta or rice), starch granules absorb water and become softer, making them more digestible. But as starch cools after cooking, some of it rearranges back into a gel-like structure--a process called ‘starch retrogradation’. This turns some of the starch into ‘resistant starch’, a type of fibre.
Resistant starch escapes digestion and reaches your gut microbes intact, who break it down and use it for energy. And here’s the cool part: when microbes break down resistant starch, they produce short-chain fatty acids (SCFAs)— compounds with anti-inflammatory benefits that support a healthy gut environment. SCFAs also play a role in helping us feel full and regulating appetite.
In addition to foods naturally high in resistant starch—like oats, pulses and greenish bananas—studies show that cooked and cooled noodles, rice, potatoes, and lentils contain more resistant starch than their freshly cooked versions. That means saving leftover starchy foods (or cooking a bit extra) and turning them into the next day’s lunch or dinner could benefit your gut microbes.
Here’s my top 5 tips
- When you’re cooking pasta, lentils, rice or potatoes, cook some extra for the next day’s lunch.
- Cool your starchy food quickly and safely by cooling with cold water, dividing into small containers, and storing in the fridge. This is especially important with rice, which can be a high risk food if not cooled quickly*.
- Reheating doesn’t seem to destroy RS, so if you want to reheat go ahead, but be sure to follow the safe reheating guidelines for rice, and eat any leftover rice within 24 hours of cooking*.
- Choose wholegrain varieties of rice and pasta to benefit from other types of fibre as well as resistant starch
- Need a leftover idea? Try my soba noodle salad with peppers, peas, and miso dressing—perfect for lunchboxes.
*To learn more about cooling and reheating rice safely, read this guidance from the Food Standard Agency.
Read more from our fact v fiction series
You don't need grains for fibre?
The truth behind 7 common bloating claims
Ultra-processed foods: Are they really harmful
Glucose spikes and gut health - what you need to know
Sources
Harnessing the power of resistant starch: a narrative review of its health impact and processing challenges. Frontiers in Nutrition. (2024). Link.
Effect of cooling of cooked white rice on resistant starch content and glycemic response. Asia Pacific Journal of Clinical Nutrition. (2015). Link.
The Effect of Cooking and Cooling Chickpea Pasta on Resistant Starch Content, Glycemic Response, and Glycemic Index in Healthy Adults. Metabolites. (2024). Link.
Method of food preparation influences blood glucose response to a high-carbohydrate meal: A randomised cross-over trial. Foods. (2020). Link.
Why Leftover Christmas Dinner is Better for You. (Retrieved April 28, 2025). Link.
